ARTHROPODA 273 



Mouth-parts. These are complicated and demand careful study, if satis- 

 factorily made out. Remove the labrum and proceed from before, 

 backward. 



Mandibles; a pair of horny tooth-bearing jaws. Draw in position. 

 Maxilla; a pair of compound jointed organs made up of three portions, 



the lacinia (nearest the median line), the galea, and the maxillary 



palpus (external). 

 Labium or lower lip; this also bears a palpus. The labium may be 



studied and removed before the study of the maxillae. 

 Tongue. 



How many segments seem to be represented in the head? Evidences. 

 Internal structure. 



Select large female specimens preferably. Clip the wings close to the 



body, and pin the specimen to a board, dorsal surface upward. 

 With a pair of fine, sharp pointed scissors make a longitudinal incision 



into the integument of the abdomen near each side. Gradually and 



carefully remove the skin between the cuts from behind forward. 



Look for the heart, a long, thin-walled, mid-dorsal vessel, which if 



not removed with the skin may be seen just beneath it. Unroof both 



the abdomen and thorax. Note the exposed muscles of the thorax, 



also the whitish fat bodies next the body wall. 



1. Trachea. If the specimen is freshly killed the tracheae will be filled with 

 air and will show as white, glistening tubes. Seek their connection with 

 the spiracles, and note their ramification and unions in the body. Isolate 

 some of the smaller branches and study under the microscope. Prove 

 that they are tubes. How kept open? 



2. Reproductive Organs. (These are much more difficult in the male.) 

 Ovaries: In how many masses? Notice the subdivisions of the ovaries. 



These contain the eggs and communicate by means of an oviduct 

 with the outside. In what segment? Examine an ovum with the 

 microscope. Mash, and notice the yolk. 



3. How do the muscles of the thoracic region differ from those in the 

 abdominal? Are the fibres plain or striate? 



4. Digestive Tube. 



Dissect forward into the head, and press the other organs aside so that 

 the course of the tract may be revealed. It consists of the following 

 parts, which should be identified: 

 Mouth. 



Esophagus; size and course. 



Crop (an enlargement of the esophagus); shape, position. 

 Stomach; character and extent. (At the anterior end is a ring of 

 tubular appendages which are glandular in function, the gastric 

 caeca; at the posterior end it is limited by a circle of fine tubes 

 Malpighian tubules which are excretory.) 

 Intestine; length, course and size. 

 Anal opening; position. 



Make drawing of digestive tract from side view, showing in outline the 

 body regions and the relation of the portions of the tract to these. 



5. Nervous System. (Remove the alimentary tube and examine the floor 



of the abdominal cavity.) 

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